1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, and more particularly, to a semiconductor integrated circuit having a shield wire.
2. Description of the Related Art
Throughout the development of high-speed computer systems, research into the enhancement of data processing speed of semiconductor integrated circuits has been continuous and vigorous. With ever-increasing data processing speed, designers are faced with the challenges of containing the increased interference between signal conductors, and of controlling increased noise generated during circuit operation. Thus, in order to maintain operating margins during high-speed operation, it is increasingly important to properly shield the generated interference and noise from primary signal conductors in order to avoid improper signal transitions.
FIG. 1 illustrates a first conventional technique for signal wire shielding in a semiconductor integrated circuit. In this example, neighboring signal conductors or wires 14 and 16 to be shielded are isolated from each other by a shield wire 12 electrically coupled to an external voltage source 10. The external voltage source in turn applies a positive or negative source voltage or a ground voltage to the shield wire. The stable voltage serves as a barrier to noise and interference.
FIG. 2 illustrates a second conventional technique for signal wire shielding in a semiconductor integrated circuit. In this example, the signal wire 24 is electrically coupled to a first terminal of a decoupling capacitor 22, and a second terminal of the decoupling capacitor 22 is electrically coupled to an external voltage source 20. In this configuration, any noise components induced on the signal wire 24 by noise and interference generating sources are applied to, and absorbed by, the external voltage source 20 or the ground port, and therefore are prevented from adversely affecting nearby signal wires.
During operation, the voltage applied by the external voltage source can vary due to corresponding variances in operating current. As a result, in the conventional shielding configurations of FIGS. 1 and 2, instead of noise suppression, noise can be actively introduced on the signal wires 14,16 via shield wire 12 (FIG. 1) or on signal wire 24 via decoupling capacitor 22 (FIG. 2). This, in turn, can cause the device to exhibit a reduced operating margin or worse, cause the device to malfunction.